The unknown is a lovely source of joy and wonder, but it has several dimensions. In particular, some unknowns are mysteries, whereas others are mere secrets.

In essence a secret is simply a puzzle. Somebody else has the answer; they've just hidden it and won't tell us where to find it. Unveiling a secret gives a quick thrill, but there's no lasting compensation. Secrets can be cute, clever things, maybe even temporarily valuable things, but they're by nature finite. Governments and corporations and individuals expend vast resources to keep their own secrets, and to attempt to unravel others' secrets. So what?

In contrast, a mystery is a problem, a challenge that has depth, staying-power, mana. What governs the large-scale structure of spacetime? Where are the sources of values, of good and bad, right and wrong? What are the limits to computability? Whom should we trust, love, and obey? What forces drive history? Where do the fundamental particles of the universe come from? What's the meaning of life? Why?

Nobody knows the answer to a true mystery. Perhaps nobody will ever know; the best mysteries have wheels within wheels, never-ending levels of ever-changing complexity. But wrestling with a good mystery repays us with learning, partial solutions, maybe glimpses of a Holy Grail that we will never touch. Secrets can be useful as warm-up exercises --- but secrets only tease. Mysteries endure.